1. Field of the Invention
The present invention relates to film condensers and metalized films for manufacturing the film condensers.
2. Description of Related Art
Film condensers are generally manufactured by preparing first and second plastic films on which a thin metal layer is deposited, placing the second film on the first film, rolling up the stacked films so as to form a cylindrical body, and forming a pair of terminal electrodes at both ends of the cylindrical body by thermal spraying.
Recently, for the purpose of improving safety, film condensers having a fuse function have been put to practical use. In such a film condenser with a fuse function, a plurality of uncoated portions are formed in a metal coating layer of at least one of the two metalized films so that the metal coating layer is divided into a plurality of rectangular electrode regions and narrow fuse portions electrically connecting each electrode region to one of the terminal electrodes. According to the film condensers of this type, should a short circuit occur between the electrode regions of the first and second metalized films, the fuse portion will instantly evaporate due to the heavy current passing therethrough, the supplement of the current to the area including the short circuit point can thereby be stopped.
In this type of film condenser, because at least one electrode region becomes incapacitated whenever a short circuit occurs in the condenser, the capacitance of the condenser will be gradually decreased. Furthermore, the breaking down of the fuse portions is likely to be occurred for other reasons, for example, by a corona discharge generated between the metal layers of the first and second metalized films. Therefore, the decrease ratio of the capacitance in the film condenser having a fuse function is relatively large, and it is desired to reduce the capacitance decrement generated by each brake down of the fuse portion.
In order to achieve this object, Japanese Patent Application, First Publication, No. Hei 4-225508 discloses a film condenser in which the area of the electrode regions is reduced by arranging a plurality of rectangular electrode regions in a lattice pattern. Each of the four corners of each electrode regions is connected by a fuse portion to the adjacent three corners of other electrode regions. That is, each fuse portion simultaneously connects four electrode regions.
However, in a film condenser of this type, when one of the fuse portions breaks down due to a short circuit, the fuse portions locating adjacent to the cut fuse portion are likely to break down, as if it is a chain reaction, due to the electrical shock. Therefore, in spite of small area of the electrode regions, the decrease of the capacitance which occurs at every break downs of the fuse portion cannot be improved in comparison with the conventional one.